I always thought it would be cool if we counted time in units that were multiples of ten of each other. This is known as decimal time. There'd be 100 seconds in a minute, 100 minutes in an hour, and ten hours in day. A recent Twitter conversation got me thinking about this again.

The problem with this idea is that it requires the second to be redefined. To be sure, there are other problems, too, like how do you convince six billion people to change their notion of what seconds, minutes, and hours are?

But changing the length of a second means changing a lot of scientific constants, and that's a pretty serious undertaking. It would be better to start with the existing unit of a second (which, incidentally, is a metric unit), and build on top of that.

So, let's put aside the actual labels we'll give each of these units, and let's keep a second a second. Now let's put 100 seconds in a minute, 100 minutes in an hour, and that gives us 8.64 hours in a day. That's not a very nice, round number. How important is it that it be a "nice" number, though?

On Earth, the average day is 86,400 seconds long. On Mars, the average day (sol) is 88,775 seconds. In our decimal time units, that would be 8.86 hours. On Earth's moon, a day is 2,551,443 seconds long, or 255.1 hours (are you starting to see the advantage of decimal time?). Obviously, as our species spreads out to other celestial bodies, having an even number of hours in the day everywhere will impossible, because not all days will be the same duration.

So, let's compare some other durations:

Duration Traditional Units Decimal Time
Second 1 s 1 s
Traditional Minute 1 m 0.6 m
Traditional Hour 1 h 0.36 h
Day 24 h 8.64 h
Shower 15 m 0.36 h
Typical Work Day 8 h 2.88 h
Lunch 1 h 0.36 h
Movie 2 h 0.72 h

Yuck! The problem with decimal time based on the existing second is that there are no conveniently-sized units for most day-to-day human activity.

The quarter-hour, or 15 minutes, is 900 seconds. That's nearly 1000 seconds, so perhaps the kilosecond would be a convenient unit. Ten kiloseconds would be a little over 2 h 45 m traditional, so maybe we're on to something here.

Duration Traditional Units Kilseconds
Kilosecond 0.27 h, 16.6 m 1 ks
Traditional Hour 1 h 3.6 ks
Decimal Hour 2.78 h 10 ks
Day 24 h 86.4 ks
Shower 15 m 1 ks
Typical Work Day 8 h 29 ks
Lunch 1 h 4 ks
Movie 2 h 7 ks

I've rounded the kilosecond times for the activities, because their durations aren't very precise to begin with. It seems like the kilosecond could be a fairly convenient unit, after all.

Now we just need to find good names for these decimal units. Seconds are fine, but the rest need new names that are easy to say, abbreviate acceptably to unit labels, and don't sound cheesy (the old Battlestar Galactica used "centons," and I never did figure out how much time that represented).

We might also ponder how one writes decimal time. Traditionally, in the U.S. and other parts of the world (but definitely not all!), a time of day (or duration) is written as double-digit numerals separated by colons: 12:37:58. Decimal time can be written much more simply, as decimal hours in the day: 4.548. Now, imagine you want to add (in traditional units) 4 minutes and 22 seconds to 12:37:58. Try it. It sucks. But adding 262 seconds to 4.548 decimal hours is much easier: 4.548 h + 0.0262 h = 4.574 h.

It may seem weird, but if you grow up with these units, and everything around you uses them, they'd be obvious, and the units we use today would seem strange.


Metric time. (2011, February 17). In Wikipedia, The Free Encyclopedia. Retrieved 05:51, March 27, 2011, from http://en.wikipedia.org/w/index.php?title=Metric_time&oldid=414432996

Timekeeping on Mars. (2011, January 15). In Wikipedia, The Free Encyclopedia. Retrieved 05:52, March 27, 2011, from http://en.wikipedia.org/w/index.php?title=Timekeeping_on_Mars&oldid=408111863.

Lunar day. (2011, March 17). In Wikipedia, The Free Encyclopedia. Retrieved 05:53, March 27, 2011, from http://en.wikipedia.org/w/index.php?title=Lunar_day&oldid=419235268.